1. Field of the Invention
The invention is concerned with novel antitumor/antibiotic compounds related to dynemicin which contain a core tetrahydroquinoline enediyne structure and to novel methods of synthesis of analogs and derivatives of these compounds. Also disclosed are pharmaceutical compositions employing various of the new compounds as antitumor agents.
2. Description of Related Art
Enediyne anticancer antibiotics are a recently discovered class of compounds with potent biological activities. This class of compounds includes neocarzinostatin, esperamicin, and, more recently, dynemicin, as well as calicheamicin. The enediyne moiety is a bicyclo [7.3.0]dodecaenediyne chromophoric system. The unusual molecular architecture contributes to the exceptional biological activity and mode of action of enediyne compounds which are believed to exert their effect as DNA cleaving compounds operating through a free radical mechanism. Such cleaving properties are derived from the ability to generate Sp.sup.2 carbon centered radicals after activation (Nicolaou and Dai, 1991).
The different groups of enediyne anticancer antibiotics exhibit similar biological activities, but may differ significantly in target and toxicity. Neocarzinostatin was originally isolated from a culture of Streptomyces carzinostaticus. Compounds of this class exhibit potent antitumor antibacterial action. The calicheamicins are isolated from Micromonospora echinospora ssp. calichensis. This subclass of compounds is highly active against both gram positive and gram negative bacteria and also exhibits unusual high activity against murine tumors such as P338, L1210 leukemias and solid neoplasms such as COLN26 and B-16 melanoma. Esperamicins have been isolated from cultures of Actinomadura verrucosospora and are similar in their activities to the calicheamicins. Structurally, the esperamicins contain a bicyclo [7.3.1]tridecaenediyne ring system, an allylic trisulfide (or tetrasulfide), a 1,5-diyn-3-ene moiety as pan of the ring system, and an .alpha.,.beta.-unsaturated ketone in which the double bond is at the bridgehead of the bicyclic core. These compounds are extremely potent anticancer agents and exhibit activity against several murine tumor models, including P388, B16, and 5076.
A more recently discovered class of enediynes are the dynemicins. These violet-colored antibiotics were isolated from fermentation cultures of Micromonospora chersina. Studies in vitro and in vivo have demonstrated that these compounds are active against a variety of cancer cell lines. They have been shown to significantly prolong the life of mice inoculated with P388 leukemia and B16 melanoma cells. The dynemicin family of compounds combines low toxicity with good in vivo antibacterial activity. Deoxydynemicin, like the parent dynemicin, is also biologically active. Structurally, the dynemicins include a ten-membered ring with a 1,5-diyn-3-ene bridge; however, they differ structurally from other related families in having an anthraquinone chromophore.
1,5-diyn-3-ene antibiotics have generated considerable interest and challenge to synthesize new active compounds which have the unique 1,5-diyn-3-ene core. Several reports have indicated successful synthesis of the core diyne structure. Calicheamicinone has been totally synthesized (Hazeltine et al., 1991). The synthesis employed application of the Becker Alder reaction to obtain an appropriately substituted brominated benzaldehyde, an in situ protection, and an intramolecular Emmons-like closure in an annulation procedure. The final product, calicheamicinone, represents the aglycone moiety of calicheamicin .gamma.-1 and esperamicin a.sub.1.
The aglycon portion of calicheamicin .gamma.-1 has also been synthesized (Smith et al., 1992). In that synthetic approach, the molecule was synthesized via an intramolecular alkenyl nitrile oxide dipolar cycloaddition reaction leading directly to incorporation of the full functionality of the aglycon.
Other approaches to the synthesis of the ene-diynes of esperamicin/calicheamicin have provided a synthesis of 2-ketobicyclo [7.3.1]enediyne and 13-ketocyclo [7.3.1]enediyne through the use of .eta..sup.2 dicobalt hexacarbonyl, alkyne complexes. This synthesis is based on complexing the 10,11-acetylenic bond with a dicobalt hexacarbonyl compound (Magnus and Fortt, 1991).
Several approaches to a simple and efficient route to a dynemicin A model system have been reported. In contrast to the above strategies, a transannular Diels-Alder route has resulted in polycyclizations to dynemicin-type molecules (Porco et al., 1990). Other synthetic routes have been reported (Nicolaou et al., 1990). Two novel dynemicin A compounds containing the epoxide and the ene-diyne functionalities of the parent compound were synthesized with either hydrogen or hydroxyl at one of the bridgehead positions. Other model dynemicin A compounds have been prepared starting from 7,8,9,10-tetrahydrophenanthridine. The compounds produced in these syntheses were N-protected derivatives (Nicolaou et al., 1991). The N-protected model systems failed to exhibit any activity when incubated with .phi.x 174 DNA. However, some activity was observed when the N protecting group was removed. The free amine was unstable although activity in crude mixtures caused double-stranded DNA cleavage similar to that observed for the parent compound dynemicin A.
An alternate synthesis of the core tetrahydroquinoline enediyne structure using .beta..sup.2 hexacarbonyl dicobalt acetylene complexes has been reported (Magnus & Fortt, 1991). An important step in this synthesis was complexation of one of the intermediates as a hexacarbonyl dicobalt complex. By employing a cation solvating solvent for the formation of the azabicyclo [7.3.0]diynene, a stable azabicyclo [7.3.1]tridecaenediyne core structure was obtained. In another approach, a transannular Dieis-Alder polycyclization and an allylic diazine rearrangement have provided an intermediate that was transformed to the ene-diyne bridged tricyclic core of diynemicin A (Wood et al., 1992).
While a number of approaches to the synthesis of enediynes and particularly aimed at the total synthesis of diynemicin A have been explored, there exists a need for analogs containing the core enediyne bridged tricyclic diynemicin A core. An improved synthesis would provide more efficient entry to novel compounds with expanded antibiotic and antitumor activities.